#define _CRT_SECURE_NO_WARNINGS 1

#include <unordered_set>
using namespace std;

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        unordered_set<int> hash;
        for (int i = 0; i < nums.size(); ++i)
        {
            if (hash.count(nums[i])) return true;
            else hash.insert(nums[i]);
        }
        return false;
    }
};